Soekris' DAC implementations

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E

Eldam

Member
Joined 2012
#1
Hi,

A thread to know how to implement : volume control, filter, casing, shielding, powersupply, etc for the discrete R2R DAC made by Soekris:

Feel free to ask and answer. Regards, Eldam
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Original Vendor thread (DAM 1021) http://www.diyaudio.com/forums/vendors-bazaar/259488-reference-dac-module-discrete-r-2r-sign-magnitude-24-bit-384-khz.html

OEM (DAM 1121) Building thread: Building with the Soekris dam1121

Currently available files for dam1021 (updates): Soekris Engineering ApS, Downloads

For a quick drawing with connections and more detailed descriptions + tweaks, : The Soekris R-2R DAC: Technical Details | H i F i D U I N O

Diyaudio WIKI : Soekris R2R DAC - diyAudio (usefull links, more to come)

Parts: some usefull parts ref and inputs given by members (thank you) :
PS traffos
62020 - 2x7AC 5VA - http://www.digikey.com/product-detai...108-ND/3881389
62030 - 2x7AC 7VA - http://www.digikey.com/product-detai...059-ND/3881371
2x7AC 10VA 70040K Talema Group LLC | 1295-1040-ND | DigiKey
2x7AC 7VA - MCFM70/07 - MULTICOMP - TRANSFORMER, TOROIDAL, 2 X 7V, 7VA | element14 Australia
2x7AC 5VA - MCFM50/07 - MULTICOMP - TRANSFORMER, TOROIDAL, 2 X 7V, 5VA | element14 Australia
Netherlands : Toroidal transformers for 115V and 230V applications
France:transformateur torique 15va 2x7v
The links are to the Australian website but it's easy enough to change location using "Change Country" at the top right of the page. The 2x7AC 5VA is also available from a UK based seller on eBay (more than 10 in stock) MCFM50 07 Multicomp Mini Toroidal 5VA 2X 7V | eBay
US: AN-0107 - 10VA 7V Transformer - AnTek Products Corp good price !

For alternative DC feeding possibility, some informations below & elswhere in the original thread: some mention noticeable difference. A simple torroid is a good enough starting point.

Pulse transformers if input Spidf (SE) choosed (Soekris's input post 41): PE-65612NL Pulse Electronics Corporation | 553-1580-5-ND | DigiKey or better (?) S22083 Newava Technology Inc | 470-1003-ND | DigiKey ; DA101C - MURATA POWER SOLUTIONS - TRANSFORMER, 1:1, 0.01H - 0.0206H, DIL | element14 Australia. Notice here than the first PE would have the best inter-windding capacitance which is the interisting point for chosing it- Dac itself has a the best jitter rejection possible due to the fifo, so jitter perf of the others pulse transformer do not matter with this DAC, so quietest noise is prefered over the best jitter perf for the input pulse transformer! Abraxalito input : read the thread)

SPIDF (AES) : Audio Note or Tribute traffos (sorry no cheaper refs yet 🙂 ! but here surely sota noise rejection... cobalt core, etc)
TOSLINK: Toshiba RX modules advised for good quality: TORX177 for 5V and TORX147 for 3.3V

Connection shematics for the SPIDF; http://www.diyaudio.com/forums/vend...magnitude-24-bit-384-khz-111.html#post4202602

Volume control (if the pot way is choosed) : "Any mono linear one from 1K to 10K, preferable high quality conductive plastic to avoid noise" (so just one mono linear pot control the two chanels) http://www.diyaudio.com/forums/digi...ris-s-dac-implementations-17.html#post4194108 : I.E. : 3851A-282-103BL - BOURNS - POT, COND PLASTIC, 10KOHM, 20%, 1W | element14 Australia or P231-QC20BR10K - BI TECHNOLOGIES / TT ELECTRONICS - POTENTIOMETRE POUR PANNEAU 10K | Farnell France

DIY H.Q connectors (to avoid shorts) J3 : 2-87456-1 - TE CONNECTIVITY / AMP - WIRE-BOARD CONNECTOR RECEPTICLE 26 POSITION, 2.54MM | element14 Australia ; J10 : 1-87499-7 - TE CONNECTIVITY / AMP - CRIMP HOUSING, 1 ROW, 10WAY | element14 Australia or :
Inputs & front panel switch board GB (for USB Amareno+ SPIDF): Input and switch boards for Soekris DAM1021 DAC

USB to Serie RS232 interface to update the DAC via a laptop: 1 Port RS232 USB to Serial Adapter - US-101 - Brainboxes - RS422/485 RS232 Serial Cards , Digitus USB auf Seriell DB9 Adapter schwarz: Amazon.de: Computer & Zubehör (PLL throughpass chip inside) / USB-to-Serial Converter - UC232A, ATEN USB Converters ;Trendnet - Convertisseur USB vers Série, TU-S9: Amazon.fr: Informatique etc ! (take care with the compatibility with W 7/8 when you buy one)

Debuging your USB to Serie interface DimDim member blog : R2R | Dimdim's Blog

Working Thread about the Digital filter improvementof the FGPA chip: http://www.diyaudio.com/forums/digital-line-level/269776-filter-brewing-soekris-r2r.html#post4224106

Output-stage Thtread: http://www.diyaudio.com/forums/digital-line-level/270014-output-stage-soekris-r2r.html#post4228899

Mother board control kit: http://www.diyaudio.com/forums/vend...soekris-dam1021-1121-control.html#post5071729
 
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#5
Sort of pre voltage regulation to help PSSR for the embeded low noise LDO ?

Does just a shunt stabilizer could give better result than a super shunt with voltage regulation (as this function is managed with sota smt ldo into the pcb ?

Or just a snubber at the secondaries if AC is used instead DC as the design allow as well ?

I read somewhere than more than a standalone common self is good for filtering.

Some put a comon self before the primary but add one after the secondarie in a Pi filter as well, sometimes mixing it wit an another Pi with no comon filter !

Soekris is ok with the measurement, what can add a more complex PS before this DAC ?

Let it simple ?
 
#7
I was going to just feed it AC, but now I'm wondering if adding a DC pre-regulator would be of any benefit.

Since the board will regulate anyway, I don't see a reason to use a fancy pre-regulator, seems like a 317 type should be fine, but I could be wrong.

I also started looking at remote controllable pots to handle volume control. Might buy a cheap ebay one.

Randy
 
#12
To those who are thinking regulating the voltage instead of just feeding it directly with the suggested transformer by Soekris:

Do you think there is a weakness in the power supply section already built-in the module? If so, doesn't this worry you about rest of the design?

Or do you think the more regulation the better?

If one would like the keep things as simple as possible, is the following configuration too simple to hear benefits of R2R architecure?

1. DAC module
2. Toroidal transformer
3. Amareno USB powered USB-to-I2S module

(I'm asking with all my due respect for you experienced diy'ers, and just trying to understand the motivation.)

Cheers.
 
#14
leehan said:
To those who are thinking regulating the voltage instead of just feeding it directly with the suggested transformer by Soekris:

Do you think there is a weakness in the power supply section already built-in the module? If so, doesn't this worry you about rest of the design?

Or do you think the more regulation the better?

If one would like the keep things as simple as possible, is the following configuration too simple to hear benefits of R2R architecure?

1. DAC module
2. Toroidal transformer
3. Amareno USB powered USB-to-I2S module

(I'm asking with all my due respect for you experienced diy'ers, and just trying to understand the motivation.)

Cheers.
Click to expand...

Søren's posts indicate that he looked at the requirements of specific sections of the DAC and then designed local regulation and filtering to allow the DAC to meet the performance specs he was aiming for.

There are low noise regulators used around the board. The references for the R2R ladders are first regulated to 5V with low noise regulators then to 4V using precision low noise op-amps, then filtered and buffered for each channel and rail.

Extra regulation might help somewhat but from what I've read and understand Søren has taken great care with the areas he has deemed critical to performance. The DAC should perform well with the AC hooked up directly. If you wanted to use a DC supply something using LM3x7's is going to be more than adequate.

The rest of the DAC appears to be designed with equal care, and Søren's 14+ years of experience designing embedded computer motherboards is apparent in the quality of the layout.

In terms of hooking up your list looks fine to me, I'm planning something similar but might add a coax SPDIF input to the list.

The design integrates isolators on the I2S inputs and a FIFO and reclocking for jitter reduction which removes the need for extra boards for these purposes.
 
#15
spzzzzkt said:
In terms of hooking up your list looks fine to me, I'm planning something similar but might add a coax SPDIF input to the list.

The design integrates isolators on the I2S inputs and a FIFO and reclocking for jitter reduction which removes the need for extra boards for these purposes.
Click to expand...

Indeed.

I'm thinking of adding a coax SPDIF input as well because every device other than my computer has an optical output. An external optical to coaxial converter may feed the coaxial input. Or another little diy project with multiple user switchable optical inputs may be easier to use and keep the DAC box uncluttered. Is adding a SPDIF input just a matter of a coaxial terminal wired to the DAC module?
 
#16
leehan said:
Indeed.

I'm thinking of adding a coax SPDIF input as well because every device other than my computer has an optical output. An external optical to coaxial converter may feed the coaxial input. Or another little diy project with multiple user switchable optical inputs may be easier to use and keep the DAC box uncluttered. Is adding a SPDIF input just a matter of a coaxial terminal wired to the DAC module?
Click to expand...

Until the documentation is ready it's bit of guess work on the exact details.

I suspect RCA/BNC -> pulse transformer -> DAC will be the way to go for coax SPDIF. There isn't too much required apart from a couple of capacitors and a resistor or two so it should be easy to build on perf board or even point to point. There are more complicated ways of doing this - Jocko's SPDIF receiver is one but requires power as it uses an IC in addition to a pulse transformer.

TOSLINK is pretty simple as the receiver only requires a power supply plus resistor and capacitor to make it work.

Apparently there will be a means of switching inputs, so if you don't need AES/EBU or coax SPDIF you could potentially dedicate two or three inputs to TOSLINK.
 
#17
spzzzzkt said:
I suspect RCA/BNC -> pulse transformer -> DAC will be the way to go for coax SPDIF. There isn't too much required apart from a couple of capacitors and a resistor or two so it should be easy to build on perf board or even point to point. There are more complicated ways of doing this - Jocko's SPDIF receiver is one but requires power as it uses an IC in addition to a pulse transformer.

TOSLINK is pretty simple as the receiver only requires a power supply plus resistor and capacitor to make it work.

Apparently there will be a means of switching inputs, so if you don't need AES/EBU or coax SPDIF you could potentially dedicate two or three inputs to TOSLINK.
Click to expand...

Excellent, thank you.
 
#18
if a 2 x 9 V AC measured at 11.3 at the output :

I have after the drop of diodes bridge : 9.6 VDC (11.3 -1.6 diodes) after the cap.

So 13.6 VDC unloaded or is it 13.6 VDC loaded ? (9.6V x 1.41).

Sorry if already asked in the main thread, I inderstand fast but one have to explain me longly 😕 !

My thought : just maid a non regulated Pi to save the first caps of the dac which are maybe not Long Life ! And secondly : a cap // on the second cap of the Pi before the DAC can help to Taylor a little the subjective sound result in relation to each system ?!

I think to : 2x9V + Snubber + diodes + Panasonic FR 25V/2000 uF (both LL and low esr) then a common smt chocke 47 uH + FR 25V/2000 uF (// with 220 uF to taylor slightly the sound : Black Gate, other polymer, etc !).

Is my calcul good ?

In the other way I ask myself if all the time constants calculated by Soren are just good at it is and maid firstly for the 7 or 8 V AC traffo feeding directly the DAC ?

Soren or others if you have the patience, please ?😱
 
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#19
Eldam said:
if a 2 x 9 V AC measured at 11.3 at the output :

I have after the drop of diodes bridge : 9.6 VDC (11.3 -1.6 diodes) after the cap.

So 13.6 VDC unloaded or is it 13.6 VDC loaded ? (9.6V x 1.41).

Sorry if already asked in the main thread, I inderstand fast but one have to explain me longly 😕 !

My thought : just maid a non regulated Pi to save the first caps of the dac which are maybe not Long Life ! And secondly : a cap // on the second cap of the Pi before the DAC can help to Taylor a little the subjective sound result in relation to each system ?!

I think to : 2x9V + Snubber + diodes + Panasonic FR 25V/2000 uF (both LL and low esr) then a common smt chocke 47 uH + FR 25V/2000 uF (// with 220 uF to taylor slightly the sound : Black Gate, other polymer, etc !).

Is my calcul good ?

In the other way I ask myself if all the time constants calculated by Soren are just good at it is and maid firstly for the 7 or 8 V AC traffo feeding directly the DAC ?

Soren or others if you have the patience, please ?😱
Click to expand...

Remember that AC voltage is specified as RMS and are sinus formed, so you always need to multiply by sqrt 2 to get Peak voltage, which will then go though bridge and loaded on the capacitor....

So if you measure 11.3V AC unloaded that would be 15.98V Peak...

So if you have an additional regular bridge rectifier then a 9V AC trafo is probably fine, but you might also want to add a small series resistor to get the voltage down a little....
 
#20
Thank you so much, My understanding is better now (so I don't keep the drop of 1.6 V due to the bridge of the DC PS I want to make in the calcul for the ending peak to peak).

Ok will swap the chocke of the Pi by a 2 W resistor of the good value to have less than 15V peak to peak (around 9 max VDC to have peak to peak something like 12.5 VDC max as advised).

So the traffo is a R-core 9V/30 VA (that's why I have only 11.3 v AC on the secondaries).

Does the time constant should be keeped with such DC PS before your DAC or do you advise better a standalone 7-8 VAC torroid traffo, despite the rude pulsed current on the first polymers of your DAC !

Two cents of me, it will sounding the same in both case with equal result ?
 
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